System and method for monitoring features of a blast

ABSTRACT

A method of monitoring a feature of a blast such as velocity of detonation (VOD) comprises the steps of providing a detonator  16.1  at a blast site  12 . Prior to the blast, a blast control signal path  20, 18.1  is utilized to communicate blast control signals to the detonator. During a period following start of the blast, a blast feature signal communication path  18.1, 20  comprising at least part of the blast control signal path is utilized to communicate a blast feature signal relating to the feature to a remote blast feature monitoring station  26 . The blast feature signal is generated by generating a monitoring signal in a conductor arrangement  18.1  connected to die detonator, utilizing a sensor outside of the housing of the detonator to sense changes in a blast feature monitoring parameter of the monitoring signal, and transmitting data relating to the changes to the station  26.

TECHNICAL FIELD

THIS invention relates to blasting systems and more particularly to amethod and system for monitoring features of a blast, for examplevelocity of detonation of a main charge.

Rock or soil blasting is usually achieved by drilling at a blast site anarray of boreholes, placing in each an initiation device or detonator,and partially filling the holes with explosives. The holes are thenusually stemmed with soil or gravel. The initiation devices are selectedand interconnected so as to allow the explosive charges in the holes tobe detonated by the initiation devices in a desired sequence. There areseveral features associated with a blast or detonation of theaforementioned kind which are of potential interest, including the timeinstant of detonation, the velocity of the detonation wave, pressures inthe detonating explosive, time of arrival and intensity of shockpressure at an adjacent hole, vertical length of the stemming in thehole, the acceleration history of the burden, ground vibration etc.Detonation velocity is one of the most commonly measured dynamicfeatures of blasting and therefore various methods and systems formonitoring or measuring the velocity of detonation of a main charge areknown. In one known approach, a special monitoring circuit is deployedwith dedicated conductors extending into the blast holes. The specialcircuit is energised by a suitable signal generated at a remote site andparameters of the signal during the blast are monitored to ascertain thevelocity of detonation. Since blasting is a violent event, the signalgeneration and monitoring devices in this known method are kept at asignificant distance from the holes in which the measurements are beingdone, and are connected to the measuring circuitry by long electricalcables. It will be appreciated that this special and dedicated circuitis contributing to the cost of the system as well as to labour and timeto prepare the blast site.

OBJECT OF THE INVENTION

Accordingly it is an object of the present invention to provide analternative method and system with which the applicants believe theaforementioned disadvantages may at least be alleviated.

SUMMARY OF THE INVENTION

According to the invention there is provided a method of monitoring atleast one feature of a blast, the method comprising the steps of:

-   -   providing at least one detonator at a blast site to cause at        least part of the blast;    -   prior to the blast, utilizing a blast control signal path        extending between a blast controller and the at least one        detonator, to communicate blast control signals to the at least        one detonator;    -   during a period following start of the blast, utilizing a blast        feature signal communication path comprising at least part of        the data blast control signal path to communicate a blast        feature signal relating to at least one feature of the blast to        a blast feature monitoring station.

In a preferred form of the method, a plurality of detonators areprovided in spaced relation at the blast site and each detonator may beassociated with a respective blast control signal path and a respectiveblast feature signal communication path.

The feature may be velocity of detonation (VOD) of a main chargeinitiated by the detonator. In a single-shot blast, other features thatmay be monitored are: time instant of start of detonation, groundvibrations, detonation or explosion pressure in a blast hole and lengthor depth of the main charge in the blast hole. In a multiple-shot blast,the feature may be any one of the aforementioned plus shock pressurecaused by detonation in an adjacent hole, delay time between start ofdetonations in adjacent holes, to name but a few.

The blast controller and the blast feature monitoring station may beprovided at a common location which is remote from the blast site. Therespective blast control signal paths may comprise respective conductorarrangements connected to each of said detonators. The respectiveconductor arrangements may branch from a trunk or main conductorarrangement connected to the blast controller.

In some forms of the method, the blast feature signal may be generatedby at least one sensor which is connected to one of the main conductorarrangement and any of the respective conductor arrangements. The atleast one sensor is preferably located outside of any detonator housing.The sensor may be in the form of a suitable transducer for generating ablast feature signal in response to pressure, acceleration, strain orany other feature of the blast.

The blast feature signal generated by the at least one sensor may betransmitted to the blast feature monitoring station via the blastfeature signal communication path comprising at least part of the mainconductor arrangement. Alternatively, the blast feature signalcommunication path may comprise at least part of a conductor arrangementto which the at least one sensor is connected, and a wireless link.

Other forms of the method may comprise the steps of generating amonitoring signal in a respective conductor arrangement and sensing achange in a blast feature monitoring parameter of the signal as a resultof the blast, to provide the blast feature signal.

The monitoring signal may comprise a first signal and a second signal,such as a reflection of the first signal on the conductor arrangement.The blast feature monitoring parameter may relate to a difference incorresponding signal parameters of the first signal and the secondsignal, such as a difference in phase, amplitude and frequency.

Hence, the method may comprise the steps of causing a signal generatorto generate a first signal for propagation on the respective conductorarrangement, to cause a reflection of the first signal, and monitoringchanges in a phase and/or amplitude difference between the first signaland the reflection before, during and immediately after detonation.

The first signal may be generated by a signal generator located at theremote blast controller and which is connected to said respectiveconductor arrangement by said main conductor arrangement.

Alternatively, the first signal may be generated in the respectiveconductor arrangement by a signal generator located at the remote blastcontroller and data relating to the change may be transmitted from asensor connected to the respective conductor arrangement via a wirelesslink to the remote blast feature monitoring station.

Further alternatively, the first signal may be generated by a signalgenerator connected directly to the respective conductor arrangement anddata relating to the change may be transmitted by a sensor connected tothe conductor arrangement via a wireless link to the remote featuremonitoring station.

Also according to the invention there is provided a method of monitoringa feature of a blast, the method comprising the steps of:

-   -   providing a conductor arrangement connected to a detonator and        which detonator causes part of the blast;    -   generating a monitoring signal in the conductor arrangement;    -   sensing a change in a blast feature monitoring parameter of the        signal as a result of the blast; and    -   processing data relating to the change for providing data        relating to the feature.

The feature may be velocity of detonation (VOD) of a main chargeinitiated by the detonator and at least part of the conductorarrangement may be embedded in the main charge.

The conductor arrangement may be connected to the detonator to controlthe detonator, for example by transmitting at least one of programmingdata, a fire signal and power to the detonator from a remote source,such as a blast controller. The conductor arrangement may comprise apair of twisted conductors.

The monitoring signal may comprise a first signal and a derivativesignal, such as a reflection of the first signal on the conductor. Theblast feature monitoring parameter may relate to a difference betweencorresponding signal parameters of the first signal and the derivativesignal, such as a difference in phase, amplitude and frequency.

A presently preferred form of the method comprises the steps of causinga signal generator to generate a first signal for propagation on theconductor arrangement to cause a reflection of the first signal, andmonitoring changes in a phase and/or amplitude difference between thefirst signal and the reflection before, during and immediately afterdetonation.

In a first form of the method, the first signal may be generated by asignal generator at a remote blast controller which is connected to saidconductor arrangement by a main conductor arrangement.

In a second form of the method, the first signal may be generated by asignal generator at the remote blast controller and data relating to thechanges is transmitted from a sensor connected to the conductorarrangement via a wireless link to a remote blast feature monitoring anddata processing station.

In a third form of the method, the first signal may be generated by asignal generator connected directly to the conductor arrangement anddata relating to the changes is transmitted by a sensor connected to theconductor arrangement via a wireless link to a remote blast featuremonitoring and data processing station.

According to another aspect of the invention, a system for monitoring atleast one feature of a blast comprises:

-   -   at least one detonator located at a blast site to cause at least        part of the blast;    -   a blast control signal path extending between a blast controller        and the at least one detonator, to communicate blast control        signals to the at least one detonator;    -   a sensor sensitive to a feature of the blast;    -   a blast feature signal communication path comprising at least        part of the blast control signal path to transmit a blast        feature signal relating to the feature of the blast to a remote        blast feature monitoring station.

The sensor is preferably located outside a housing of the at least onedetonator.

The sensor may comprise a separate device connected to a conductorarrangement which is connected to the detonator. In other embodiments,the sensor may comprise at least part of said conductor arrangementconnected to the detonator.

Further according to the invention there is provided a system formonitoring a feature of a blast, the system comprising:

-   -   a detonator for causing at least part of the blast;    -   a conductor arrangement connected to the detonator for        controlling operation of the detonator;    -   a monitoring signal generator arranged to generate a monitoring        signal in the conductor arrangement; and    -   a sensor for sensing changes in a blast feature monitoring        parameter of the monitoring signal as a result of the blast.

The sensor is preferably located outside a housing of the detonator.

In a first embodiment of the system the signal generator is connected tothe conductor arrangement by a main conductor arrangement extendingbetween the conductor arrangement and the signal generator.

The signal generator may form part of or be connectable to a blastcontroller.

The sensor may comprise a sensing circuit forming part of or which isconnectable to the blast controller.

In a second embodiment the sensor may be connected directly to theconductor arrangement and data relating to the changes may betransmitted by the sensing circuit via a wireless link to a remote blastfeature monitoring and data processing system.

The sensor may be connected to the main conductor arrangement at a pointwhere the conductor arrangement branches from a main conductorarrangement.

In a third embodiment the signal generator and the sensor may beconnected directly to the conductor arrangement and the data relating tochanges in the blast feature monitoring parameter may be transmitted viaa wireless link from the sensor to a remote blast feature monitoring anddata processing system.

The conductor arrangement and the main conductor arrangement maycomprise a pair of twisted conductors.

The wireless link may comprise an RF transceiver at both ends hereof.

BRIEF DESCRIPTION OF THE ACCOMPANYING DIAGRAMS

The invention will now further be described, by way of example only,with reference to the accompanying diagrams wherein:

FIG. 1 is a block diagram of a first embodiment of a detonation systemcomprising a blast feature monitoring system according to the inventionin the form of a VOD measurement system;

FIG. 2 is a block diagram of a second embodiment of the system accordingto the invention;

FIG. 3 is a block diagram of a third embodiment of the system accordingto the invention;

FIG. 4 is a basic block diagram of part of a VOD measurement system;

FIG. 5 depicts waveforms measured at points A and B in FIG. 4, beforedetonation of a main charge;

FIG. 6 depicts similar waveforms during a period from before detonation,during detonation until after the detonation;

FIG. 7 depicts similar waveforms on a smaller time scale during thedetonation; and

FIG. 8 depicts similar waveforms also on the smaller time scale, buttowards the end of the detonation.

DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION

In FIG. 1 there is shown a block diagram of a first embodiment of adetonation system comprising a blast feature monitoring system accordingto the invention in the form of a velocity of detonation (VOD)measurement system designated by the reference numeral 10.

The detonation system is shown deployed at a blast site 12 defining aplurality of blast holes 14.1 to 14.n. In each of the holes there isprovided an electric, alternatively and electronic detonator 16.1 to16.n respectively. Each detonator 16.1 to 16.n is connected via arespective branch or “down the hole” lead conductor arrangement 18.1 to18.n to main lead conductor arrangement 20 which in turn is connected toa blast controller 22. Each lead conductor arrangement 20 and 18.1 to18.n preferably comprises a known twisted pair of conductors.

Each of holes 14.1 to 14.n is filled with a respective body 24.1 to 24.nof a main charge. The conductor arrangements 18.1 to 18.n are at leastpartially embedded in respective bodies 24.1 to 24.n. The body of maincharge may comprise any one or more of known emulsion explosives, ANFO,blends thereof, nitroglycerin and watergell explosives. It is known thatonce a main charge is detonated by the detonator 16.1 in known manner,the detonation propagates in the body of main charge as shown at C. Thespeed of propagation is referred to as the velocity of detonation (VOD)and is measured in meters per second or feet per second.

In use, the detonators 16.1 to 16.n are programmed and/or controlled byblast controller 22 in known manner by transmitting control andprogramming data, such as delay time data, on conductor arrangements 20and 18.1 to 18.n which constitute a blast control signal path to eachdetonator. Power is also transmitted to the detonators to be stored onrespective local charge storage devices (not shown). A common“fire”-signal is then transmitted on the aforementioned control signalpaths. Upon receipt of the “fire”-signal, and also in known manner, eachdetonator starts to process respective delay time data. At the end of arespective delay time, a fuse in the detonator is energized by chargestored on the charge storage device, to cause detonation. As statedhereinbefore, the detonation propagates as shown at C and in the processdisintegrates at least part of the respective branch conductorarrangement 1 8.1.

A VOD measurement system 26 according to the invention utilizes changesin one or more blast feature monitoring parameters of a monitoringsignal transmitted on the conductor arrangements 20 and 18.1 to 18.n andwhich act as a blast feature transducer or sensor, to determine the VOD,as will hereafter be described. Such monitoring parameters may includephase, amplitude, frequency etc or changes in differences between valuesof similar signal parameters of a first signal and a second orderivative signal, such as a reflection of the first signal on theconductor arrangement. The blast controller 22 and the blast featuremonitoring station 26 are provided at a common location remote from thelast site.

In FIG. 4 there is shown a block diagram of part of one example of a VODmeasurement system 24 falling within the scope of the present invention.

The system comprises a monitoring signal generator 27 which is connectedto the main lead conductor arrangement 20. The monitoring signal issensed at point A at a blast feature monitoring station 26 and connectedvia suitable circuitry 28 to a waveform recorder in the form of anoscilloscope 30, for example. Signals on line 20 are also sensed atpoint B and fed via circuitry 32 to the recorder 30. At the monitoringstation, resulting signals are reproduced for comparison and analysis.This comparison and analysis may be computerized and may yield outputdata relating to various features of a blast, including VOD.

In FIG. 5 there are shown typical waveforms at points A and B beforedetonation. As will be clear, the monitoring signal at A is in the formof a sine wave having a frequency of about 150 kHz. The second signal atpoint B represents a reflection on the conductor arrangements. It willbe seen that there is an initial phase difference ΔØ₁ between the twosignals as well as an initial amplitude difference ΔA₁. It has beenfound that these differences are proportional to the length of theconductor arrangements 18.1 and 20. It has also been found that for theconductor arrangements used in an experiment, a phase difference of15-20 degrees represents a length of about 30 meters.

In FIG. 6, there are shown the waveforms at A and B, before, during andafter the detonation. Start of detonation is shown at point 36 and endof detonation is shown at point 38. The detonation propagates throughthe charge body during period 34, as hereinbefore described.

In FIG. 7 there are shown the signals at A and B during part of period34, but on a smaller time base. A change in amplitude of the signal at Bis clearly visible as is a charge in the aforementioned initial phasedifference ΔØ₁.

In FIG. 8 there are shown the waveforms at A and B towards the end ofperiod 34 and after the end of detonation at point 38.

After point 38, the phase difference is ΔØ₂ and which has beendetermined to indicate a conductor arrangement length of 28 meters. Thetime period 34 of detonation is determined at 240 μs. Similarmeasurements for the length of the conductor arrangements may be made onthe bases of changes in the difference between the amplitudes ΔA₂-ΔA₁.

The VOD is determined by: $\begin{matrix}{{The}\quad{VOD}\quad{is}\quad{determined}\quad{by}\text{:} = \frac{{change}\quad{in}\quad{conductor}\quad{arrangement}\quad{length}}{{time}\quad{period}\quad 34}} \\{= \frac{2\quad m}{240\quad{\mu s}}} \\{= {8333\quad m\text{/}s}}\end{matrix}$

In FIG. 2 there is shown another embodiment of the VOD measurementsystem according to the invention. In this embodiment data relating toblast feature monitoring parameters derived from a monitoring signalpropagating in conductor arrangement 18.1 is transmitted via a wirelesslink 40.1 by sensor 42 connected to conductor arrangement 18.1 to themonitoring station in the form of a VOD data processing system 44.Similarly data relating to similar parameters derived from a monitoringsignal propagation in conductor arrangement 18.2 is transmitted bysensor 46 via wireless link 40.2 to the VOD data processing system 44.

In FIG. 3 there is shown a system wherein main lead conductorarrangement 20 for conveying programming data, power and the“fire”-signal to the detonators 16.1 to 16.n is replaced by a wirelesssystem.

As in the case of the system in FIG. 2, data relating to the blastfeature monitoring parameters is transmitted via a wireless link 50 toVOD data processing system 44 by sensor 52 which is connected toconductor arrangement 18.1. The monitoring signal may be generated by asignal generator (not shown) forming part of sensor 52.

It will be appreciated that other aspects or features of a blast orshots in a multi shot blast may also be monitored and/or measured byutilizing monitoring parameters and changes in monitoring parameters ofa monitoring signal. Such aspects include: time instant of start ofdetonation, shock pressure from detonation in adjacent hole, groundvibrations, detonation or exploration pressure in a hole, delay betweendetonations in adjacent holes, length of main charge body, etc.

Referring again to FIG. 1, in other embodiments a separate transducer orsensor located outside the housing of any detonator may be utilized togenerate the blast feature signal. In these embodiments the transduceris connected to the main conductor arrangement 20 or to a respectivebranch conductor arrangements 18.1 to 18.1n as shown, so that a blastfeature signal communication path for transmitting the blast featuresignal to a remote blast feature monitoring station, such as VODmeasurement system 26, comprises at least part of a data control signalpath 20, 18.1 to 18.n extending between the blast controller 22 and thedetonators.

1. A method of monitoring at least one feature of a blast, the methodcomprising the steps of: providing a detonator in at least one detonatorhole region at a blast site to cause a respective shot of the blast;prior to the blast, utilizing a blast control signal path extendingbetween a blast controller and the at least one detonator hole region,to communicate blast control signals to the at least one detonator holeregion; during a period following start of the blast, utilizing a blastfeature signal communication path extending from said at least onedetonator hole region to communicate a blast feature signal relating toat least one feature of the respective shot of the blast to a blastfeature monitoring station.
 2. A method as claimed in claim 1 wherein aplurality of detonators are provided in spaced relation at the blastsite and wherein each detonator is associated with a respective blastcontrol signal path and a blast feature signal communication path.
 3. Amethod as claimed in claim 1 wherein the feature is velocity ofdetonation (VOD) of a main charge initiated by the detonator.
 4. Amethod as claimed in claim 1 wherein the blast controller and the blastfeature monitoring station are provided at a common location which isremote from the blast site.
 5. A method as claimed in claim 2 whereinthe respective blast control signal paths comprise respective conductorarrangements connected to each of said detonators.
 6. A method asclaimed in claim 5 wherein the respective conductor arrangements branchfrom a main conductor arrangement connected to the blast controller. 7.A method as claimed in claim 6 wherein the blast feature signal isgenerated by at least one sensor which is connected to one of the mainconductor arrangement and any of the respective conductor arrangements.8. A method as claimed in claim 7 wherein at least one sensor is locatedoutside of any detonator housing.
 9. A method as claimed in any one ofclaims 6 to 8 wherein the blast feature signal communication pathcomprises at least part of the main conductor arrangement.
 10. A methodas claimed in claim 7 or 8 wherein the blast feature signalcommunication path comprises at least part of the respective conductorarrangements to which the at least one sensor is connected, and awireless link.
 11. A method as claimed in claim 5 comprising the stepsof generating a monitoring signal in a respective conductor arrangementand sensing a change in a blast feature monitoring parameter of thesignal as a result of the blast, to generate the blast feature signal.12. A method as claimed in claim 11 wherein the monitoring signalcomprises a first signal and a second signal, and wherein the blastfeature monitoring parameter relates to a difference in correspondingsignal parameters of the first signal and the second signal.
 13. Amethod as claimed in claim 12 wherein the first signal is generated by asignal generator located at a remote blast controller and which isconnected to the respective conductor arrangement by a main conductorarrangement and which is also connected to the blast feature monitoringstation.
 14. A method as claimed in claim 12 wherein the first signal isgenerated in the respective conductor arrangement by a signal generatorlocated at the remote blast controller and wherein data relating to thechange is transmitted from a sensor connected to the respectiveconductor arrangement via a wireless link to the blast featuremonitoring station.
 15. A method as claimed in claim 12 wherein thefirst signal is generated by a signal generator connected directly tothe respective conductor arrangement and data relating to the change istransmitted by a sensor connected to the respective conductorarrangement via a wireless link to the remote blast feature monitoringstation.
 16. A method of monitoring a feature of a blast, the methodcomprising the steps of: providing a conductor arrangement connected toa detonator for providing blast control signals to the detonator from aremote blast controller and which detonator causes part of the blast;generating a monitoring signal in the conductor arrangement; sensing achange in a blast feature monitoring parameter of the signal as a resultof the blast; and processing data relating to the change for providingdata relating to the feature.
 17. A method as claimed in claim 16wherein the feature is velocity of detonation (VOD) of a main chargeinitiated by the detonator.
 18. A method as claimed in claim 16 or claim17 wherein the conductor arrangement is connected to the detonator tocontrol the detonator.
 19. A method as claimed in claim 16 wherein theconductor arrangement comprises a pair of twisted conductors.
 20. Amethod as claimed in claim 16 wherein the monitoring signal comprises afirst signal and a derivative signal of the first signal.
 21. A methodas claimed in claim 20 wherein the blast feature monitoring parameterrelates to a differences between corresponding signal parameters of thefirst signal and the derivative signal.
 22. A method as claimed in claim21 comprising the steps of causing a signal generator to generate thefirst signal for propagation on the conductor arrangement, generating aderivative signal by causing a reflection of the first signal, andmonitoring changes in the difference in corresponding signal parametersof the first signal and the reflection.
 23. A method as claimed in anyone of claims 20 to 22 wherein the first signal is generated by a signalgenerator at a remote blast controller which is connected to saidconductor arrangement by a main conductor arrangement and which is alsoconnected to a blast feature monitoring station.
 24. A method as claimedin claim 22 wherein the first signal is generated by a signal generatorat a remote blast controller and wherein data relating to the changes istransmitted from a sensor connected to the conductor arrangement via awireless link to a remote blast feature monitoring station.
 25. A methodas claimed in claim 22 wherein the first signal is generated by a signalgenerator connected directly to the conductor arrangement and whereindata relating to the changes is transmitted by a sensor connected to theconductor arrangement via a wireless link to a remote blast featuremonitoring station.
 26. A system for monitoring at least one feature ofa blast comprising: a detonator in at least one detonator hole region ata blast site to cause a respective shot of the blast; a blast controlsignal path extending between a blast controller and the at least onedetonator hole region, to communicate blast control signals to the atleast one detonator hole region; a sensor at the at least one holeregion which is sensitive to a feature of the blast; and a blast featuresignal communication path extending from the at least one detonator holeregion to transmit a blast feature signal relating to at least onefeature of the respective shot of the blast to a remote blast featuremonitoring station.
 27. A system as claimed in claim 26 wherein thesensor is located outside of a housing of at least one detonator.
 28. Asystem as claimed in claim 27 wherein the sensor comprises a deviceconnected to a conductor arrangement which is connected to thedetonator.
 29. A system as claimed in claim 27 wherein the sensorcomprises at lest part of a conductor arrangement connected to thedetonator.
 30. A system for monitoring a feature of a blast, the systemcomprising: a detonator for causing at least part of the blast; aconductor arrangement connected to the detonator for controllingoperation of the detonator from a remote blast controller; a monitoringsignal generator arranged to generate a monitoring signal in theconductor arrangement; and a sensor for sensing changes in a blastfeature monitoring parameter of the monitoring signal as a result of theblast.
 31. A system as claimed in claim 30 wherein the sensor is locatedoutside of a housing of the detonator.
 32. A system as claimed in claim30 or claim 31 wherein the signal generator is connected to theconductor arrangement by a main conductor arrangement extending betweenthe conductor arrangement and the signal generator.
 33. A system asclaimed in claim 30 wherein the signal generator forms part of a blastcontroller.
 34. A system as claimed in an claim 30 wherein the sensorcomprises a sensing circuit forming part of the blast controller.
 35. Asystem as claimed in claim 30 wherein the sensor is connected directlyto the conductor arrangement and wherein the data relating to thechanges is transmitted from the sensor via a wireless link to a remoteblast feature monitoring station.
 36. A system as claimed in claim 35wherein the sensor is connected to the conductor arrangement at a pointwhere the conductor arrangement branches from a main conductorarrangement.
 37. A system as claimed in claim 30 wherein the signalgenerator and the sensor are connected directly to the conductorarrangement and wherein the data relating to changes in the blastfeature monitoring parameter is transmitted via a wireless link from thesensor to a remote blast feature monitoring station.